The repair response of Escherichia coli K-12 to bleomycin was examined in Rec- mutants showing differential sensitivity to this agent. Sedimentation analysis of the cellular DNA showed incision after bleomycin treatment. The subsequent reformation of the DNA, found in the wild-type and the recD mutant, was abolished in the recB and delayed in the recF and recBC sbcB mutants. The bleomycin-induced SOS response was reduced in strains containing recB or recBC sbsB mutations. It is suggested that the RecBCD pathway has the main role in the efficient repair of bleomycin-induced DNA damage.